1. Field of Invention
This invention is directed to fluid ejection devices and methods for forming fluid ejection devices.
2. Description of Related Art
Various mechanisms are known for practicing inkjet printing. Mass production of inkjet printheads, however, can be quite complicated and expensive. For example, according to some techniques, it is necessary to manufacture an orifice plate or nozzle plate separately from an ink supply and ink ejection actuator, and to later bond the plate to the device substrate. Employing such separate material processing steps to manufacture precision devices often adds significantly to the expense of production.
Side shooting inkjet technologies are employed in some applications, but again, manufacture of side shooting inkjet printheads is sufficiently inefficient as to make mass production undesirable. More esoteric manufacturing techniques have also been employed. For example, inkjet aperture plates can be formed by electroforming, wafer bonding, laser ablation and micro-punching, etc. Such techniques, however, also add substantial expense to the mass production of inkjet printheads and therefore increase consumer costs.
For high-quality inkjet printheads, it is necessary or desirable to have high nozzle density. Further, it is desirable that construction of the printheads be performed as simply as possible. One important strategy for simplifying construction and for increasing nozzle density is to limit the number of steps in construction and reduce the amount of misalignment between the device substrate and the aperture plate. Accordingly, it is desirable to monolithically form an ink chamber from a wafer instead of bonding a nozzle plate to a die to reduce cost and obtain high yields in production.
Where an inkjet printhead is of a mechanical type including many actuator devices, it is important to ensure that a substantial clearance is provided between an ink ejector nozzle plate and the surface of the actuator device. Unless a clearance on the order of 10-100 microns is provided, a number of problems may arise. For example, if the actuator membrane and the ink aperture plate are too close, an insufficient amount of ink flows into the ink chamber during an allowed ink refill period, and can result in ink starvation during operation. Ink starvation can result in missing droplets and/or insufficient droplet volume. Reducing jetting frequency and providing a longer ink refill period could improve performance, but such tactics are undesirable in view of their adverse impact on efforts to optimize operation speed and print quality.
The rapid advance of inkjet printing technology has changed the nature of the consumer printer market and has had significant impact on related areas of image/text production and microfluids manipulation. One of the forces that has driven the success of inkjet printers in the consumer market is the affordable cost of such devices and systems.
Of the manufacturing techniques for fabricating ink chambers including aperture plates, the most popular current approaches include wafer bonding, electro-forming and laser ablation of polymers. None of these approaches are wafer-level monolithic approaches. In view of the complexity and expense of such techniques, much effort has been expended on the development of monolithic approaches to inkjet printhead fabrication. Such efforts have focused on improving printing quality while reducing printhead cost.